Nano Technology is that branch of science which studies the behaviour of matter at atomic or molecular scale, which is about 1 to 100 nanometres (1 nm = \(10^{-9}\) meters) in dimension. The motive is to manipulate the atoms or molecule to design the superior characteristics of the product. The large percentage of the nano particles are found on the surface of the atom than its interiors and because of this reason they exhibit different characteristics than the rest of the atom when sunlight falls on them.

Energy loss in conversion

The normal solar PV cells or panels cannot convert all the incoming sun light into electrical energy as one part of the light is reflected back to the atmosphere and another is lost as a heat, which results in lower efficiency of the solar panel.

Energy at different wavelengths

As you know that the sunlight comprises of 7 colors:

Violet

Indigo

Blue

Green

Yellow

Orange

Red

The solar cells performs with different efficiency with different colors of light. This is because of the fact that each color is associated with different and unique energy levels. The energy of any color light is inversely proportional to its wavelength.

Energy \(\alpha\) 1/ wavelength (lower is the wavelength, higher is the energy)

Spectrum colours

Wavelength (nm)

Energy (Joule)

Violet

400

4.97 x 10-19

Indigo

445

4.47 x 10-19

Blue

475

4.18 x 10-19

Green

510

3.89 x 10-19

Yellow

570

3.49 x 10-19

Orange

590

3.37 x 10-19

Red

650

3.06 x 10-19

The violet light is having the highest energy levels (lowest wavelength) while the red light has the lowest energy levels (Highest wavelength) in the spectrum of light.The silicon cells are more efficient in converting higher energy blue light and less efficient in converting low energy red light into the usable energy. Moreover, the part of higher energy is lost as the excited electrons spontaneously combine with the holes and produce heat.

The quantum dots

In the silicon cells the ultraviolet energy is generally absorbed by the cell and is converted into heat but not the electricity. By integrating the layer of silicon nano-particles on to the surface of the silicon cell, can boost the overall performance of the cell and this can be done through Quantum dots technology.The quantum dots are the nano crystals of semiconductor material having finite energy in them. The energy levels and the energy band gap can be modified by changing their size. It can be said that the desired wavelength of the light can be absorbed by the quantum dots by modifying their size. This flexibility of tuning energy bang gaps to absorb any wavelength of light by changing their size, without changing the basic material, has made them quite desirable for use in solar cells.The nano particles of desired size are dispersed on the surface of the silicon cell to enhance the performance of any region (Ultra violet, white light or Infra red) of the spectrum. This nano crystal film integrated on the silicon cell will absorb more light from the desired region of the spectrum and hence result in enhanced performance in the form of more usable energy.When sun light hit the quantum dots, they produce more excited electrons which move from valence band to the conduction band. Hence, increases the efficiency of the solar cell

The potential applications of nano technology in solar PV

The nano technology enhanced solar cells can be used to design an array of solar panels which can be installed on the roof to provide electricity.

These inexpensive solar cells can be used to meet the electricity needs of the rural population of the developing countries like India.

These can be used almost everywhere for lighting, water heating, medical equipments and electrical devices.

Conclusion

The research is going on to study the several aspects of solar cells in combination of nano crystals to further increase the efficiency and reduce the manufacturing cost of the solar cells. It has the potential to become a revolutionary force for the growth of solar PV market. With this pace of development, the time is not far behind when the people will have nano-technology enhanced solar panels at their roofs.